U.S. patent application number 13/415523 was filed with the patent office on 2012-09-13 for liquid crystal display device.
This patent application is currently assigned to PANASONIC LIQUID CRYSTAL DISPLAY CO., LTD.. Invention is credited to Hidefumi ISHIBASHI, Masahiro ISHII, Masato ISHII, Masaaki KITAJIMA, Toshikazu KOUDO.
Application Number | 20120229733 13/415523 |
Document ID | / |
Family ID | 46795264 |
Filed Date | 2012-09-13 |
United States Patent
Application |
20120229733 |
Kind Code |
A1 |
ISHII; Masato ; et
al. |
September 13, 2012 |
LIQUID CRYSTAL DISPLAY DEVICE
Abstract
On a liquid crystal panel, plural areas whose number is larger
than that of temperature sensors are defined. In a memory,
temperature relation information representing a relation between an
output value of a temperature sensor and a temperature of each of
the plural areas is stored. A controller acquires the output value
of the temperature sensor and estimates, based on the temperature
relation information and the acquired output value, the temperature
of each of the plural areas. According to this configuration, the
temperature of each of the plural areas defined on the liquid
crystal panel can be obtained with a small number of temperature
sensors.
Inventors: |
ISHII; Masato; (Tokyo,
JP) ; KITAJIMA; Masaaki; (Ibaraki, JP) ;
ISHII; Masahiro; (Chiba, JP) ; KOUDO; Toshikazu;
(Hyogo, JP) ; ISHIBASHI; Hidefumi; (Osaka,
JP) |
Assignee: |
PANASONIC LIQUID CRYSTAL DISPLAY
CO., LTD.
Himeji-shi
JP
|
Family ID: |
46795264 |
Appl. No.: |
13/415523 |
Filed: |
March 8, 2012 |
Current U.S.
Class: |
349/72 |
Current CPC
Class: |
G02F 1/133382 20130101;
G09G 2320/041 20130101; G02F 2203/21 20130101 |
Class at
Publication: |
349/72 |
International
Class: |
G02F 1/133 20060101
G02F001/133 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 10, 2011 |
JP |
2011-052650 |
Claims
1. A liquid crystal display device comprising: at least one
temperature sensor; a liquid crystal panel having a plurality of
areas defined thereon, wherein number of the plurality of areas is
larger than that of the at least one temperature sensor; a memory
having temperature relation information stored therein in advance,
the temperature relation information representing a relation
between an output value of the at least one temperature sensor and
a temperature of each of the plurality of areas; and a controller
which receives an output value of the at least one temperature
sensor and estimates, based on the temperature relation information
and the received output value of the at least one temperature
sensor, a temperature of each of the plurality of areas.
2. The liquid crystal display device according to claim 1, wherein
the controller uses a plurality of relation formulas defined by the
temperature relation information to thereby estimate the
temperatures of the plurality of areas, wherein each of the
plurality of relation formulas represents the relation between the
output value of the at least one temperature sensor and the
temperature of each of the plurality of areas.
3. The liquid crystal display device according to claim 2, wherein
the memory has a plurality of coefficients stored therein as the
temperature relation information, the plurality of coefficients is
associated with the plurality of areas respectively, and the
plurality of relation formulas are defined by a fundamental
relation formula to which the plurality of coefficients are
applied, respectively.
4. The liquid crystal display device according to claim 3, wherein
the fundamental relation formula includes, as its variables, a
latest output value of the at least one temperature sensor and a
value based on a preceding output value of the at least one
temperature sensor.
5. The liquid crystal display device according to claim 4, wherein
the fundamental relation formula includes Infinite Impulse Response
Filter function which includes, as its variables, the value based
on the preceding output value of the at least one temperature
sensor.
6. The liquid crystal display device according to claim 1, wherein
the controller determines, based on information changing according
to an elapsed time since the start of driving of the liquid crystal
display device, whether or not a present time falls in a
steady-state period about temperature of the liquid crystal panel,
and the controller executes a first process for estimating
temperatures of the plurality of areas when the present time falls
in the steady-state period, and executes a second process for
estimating temperatures of the plurality of areas when the present
time does not fall in the steady-state period.
7. The liquid crystal display device according to claim 6, wherein
two temperature sensors disposed away from each other are included
as the at least one temperature sensor, and the controller uses, as
the information changing according to the elapsed time since the
start of driving of the liquid crystal display device, a difference
in output value between the two temperature sensors.
8. The liquid crystal display device according to claim 1, further
comprising a backlight unit including a light guide plate and a
light source disposed at least one side of the light guide
plate.
9. The liquid crystal display device according to claim 8, further
comprising a circuit board having the at least one temperature
sensor attached thereon and disposed along the at least one side of
the light guide plate.
10. The liquid crystal display device according to claim 9, further
comprising a rear frame made of metal and covering the rear side of
the backlight unit, wherein the circuit board is fixed to the rear
frame.
11. The liquid crystal display device according to claim 8, further
comprising a plurality of circuit boards, wherein the at least one
temperature sensor is attached to one of the plurality of circuit
boards which is closest to the light source.
12. The liquid crystal display device according to claim 8, wherein
the light source is composed of a plurality of LEDs.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application claims priority from Japanese
application JP2011-052650 filed on Mar. 10, 2011, the content of
which is hereby incorporation by reference into this
application.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a liquid crystal display
device including a temperature sensor for obtaining temperature
information of a liquid crystal panel.
[0004] 2. Description of the Related Art
[0005] As disclosed in JP 2000-356976 A, a liquid crystal display
device including a temperature sensor for detecting temperature of
a liquid crystal panel has been proposed in the related art.
Temperature information of the liquid crystal panel is used, for
example, to correct the gray-scale value of each pixel.
SUMMARY OF THE INVENTION
[0006] The temperature of a liquid crystal panel sometimes varies
depending on positions on the liquid crystal panel. For example, in
a liquid crystal display device including a backlight unit having a
light source at the edge of the backlight unit, the temperature of
a portion (area) close to the edge of the liquid crystal panel is
easily increased compared to those of the other areas. If the
temperature of each area can be detected, control with higher
accuracy is possible. However, when the same number of temperature
sensors as areas are used, the cost of the liquid crystal display
device is increased.
[0007] It is an object of the invention to provide a liquid crystal
display device in which a temperature of each of plural areas
defined on a liquid crystal panel can be obtained with a small
number of temperature sensors.
[0008] A liquid crystal display device according to the invention
includes: at least one temperature sensor; a liquid crystal panel
having a plurality of areas defined thereon, wherein number of the
plurality of areas is larger than that of the at least one
temperature sensor; a memory having temperature relation
information stored therein in advance, the temperature relation
information being defined as information for representing a
relation between an output value of the at least one temperature
sensor and a temperature of each of the plurality of areas; and a
controller which receives an output value of the at least one
temperature sensor and estimates, based on the temperature relation
information and the received output value of the at least one
temperature sensor, a temperature of each of the plurality of
areas. According to the invention, the temperature of each of the
plural areas can be obtained with a small number of temperature
sensors.
[0009] In one aspect of the invention, the controller may use a
plurality of relation formulas defined by the temperature relation
information to thereby estimate the temperatures of the plurality
of areas, wherein each of the plurality of relation formulas
represents the relation between the output value of the at least
one temperature sensor and the temperature of each of the plurality
of areas. According to this aspect, a continuously changing value
can be calculated as the temperature of each of the areas, which
can increase the accuracy of estimation of temperature. In this
aspect, the memory may have a plurality of coefficients stored
therein as the temperature relation information, wherein the
plurality of coefficients is associated with the plurality of areas
respectively, and the plurality of relation formulas may be defined
by a fundamental relation formula to which the plurality of
coefficients are applied, respectively. According to this aspect,
it is no more necessary to store in the memory the plural relation
formulas respectively corresponding to the plural areas. For
example, the plural relation formulas respectively corresponding to
the plural areas can be obtained from one fundamental
relationship.
[0010] In another aspect of the invention, the controller may
determine, the controller may determine, based on information
changing according to an elapsed time since the start of driving of
the liquid crystal display device, whether or not a present time
falls in a steady-state period about temperature of the liquid
crystal panel, and the controller may execute, as a process for
estimating temperatures of the plurality of areas, processes
different depending on whether the present time falls in the
steady-state period or the present time does not fall in the
steady-state period. According to this aspect, even if the present
time is not the steady-state period, the temperature of the liquid
crystal panel can be properly estimated. In this aspect, two
temperature sensors disposed away from each other may be included
as the at least one temperature sensor, and the controller may use,
as the information changing according to the elapsed time since the
start of driving of the liquid crystal display device, a difference
in output value between the two temperature sensors. According to
this aspect, it can be easily determined whether or not the present
time corresponds to the steady-state period.
[0011] In still another aspect of the invention, the liquid crystal
display device may further include a backlight unit including a
light guide plate and a light source disposed at least one side of
the light guide plate. According to this aspect, especially the
process for estimating a temperature for each of the plural areas
is effectively operated. Moreover, in this aspect, the liquid
crystal display device may further include a circuit board having
the at least one temperature sensor attached thereon and disposed
along the at least one side of the light guide plate. By doing
this, a correlation between the output value of the temperature
sensor and the temperature of the liquid crystal panel can be
increased. The liquid crystal display device may further include a
rear frame made of metal and covering the rear side of the
backlight unit, wherein the circuit board is fixed to the rear
frame. According to this configuration, the correlation between the
output value of the temperature sensor and the temperature of the
liquid crystal panel can be further increased. Moreover, the liquid
crystal display device may further include a plurality of circuit
boards, wherein the at least one temperature sensor is attached to
one of the plurality of circuit boards which is closest to the
light source. According to this configuration, the correlation
between the output value of the temperature sensor and the
temperature of the liquid crystal panel can be further increased.
Moreover, in this aspect, the light source may include plural LEDs.
When LEDs are used in this manner, especially the process for
estimating the temperature for each of the plural areas is
effectively operated.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a cross-sectional view of a liquid crystal display
device related to an embodiment of the invention.
[0013] FIG. 2 is a schematic view showing the rear side of a rear
frame covering the rear side of a liquid crystal panel and a
backlight unit of the liquid crystal display device.
[0014] FIG. 3 is a schematic plan view of the circuit board
illustrating positions of the screws and temperature sensor.
[0015] FIG. 4 is a block diagram schematically showing a
configuration of the liquid crystal display device.
[0016] FIG. 5 is a block diagram showing functions of a controller
of the liquid crystal display device.
[0017] FIG. 6 is a diagram showing an example of temporal change in
output value of the temperature sensor and temporal change in
actual temperature of each area.
[0018] FIG. 7 is a diagram showing a table in which plural areas
are associated with coefficients.
[0019] FIG. 8 is a diagram showing an example of temporal changes
in output value of the temperature sensor and in temperature of
each area. In this drawing, the changes since the start of driving
(time when the power is turned on) of the liquid crystal display
device are shown.
[0020] FIGS. 9A and 9B are diagrams each showing a change in
temperature of each area in a transient period. FIG. 9A shows an
example of change when the driving of the liquid crystal display
device is resumed after a long time has elapsed since the end of
previous driving (when the power is turned off) of the liquid
crystal display device. FIG. 9B shows an example of change when the
driving of the liquid crystal display device is resumed without a
time interval since the end of previous driving of the liquid
crystal display device.
[0021] FIG. 10 is a diagram showing an example of a gray-scale
value table used for the correction of gray-scale value.
[0022] FIG. 11 is a diagram for explaining a method for obtaining
coefficients for estimating a temperature of each area.
[0023] FIG. 12 is a diagram showing an example of a result of
temperature measurement conducted in determining constants.
[0024] FIG. 13 is a diagram showing another example of the
arrangement of temperature detectors for measuring an actual
temperature of the liquid crystal panel.
[0025] FIG. 14 is a schematic view showing the rear side of a rear
frame included in a liquid crystal display device of another
example.
DETAILED DESCRIPTION OF THE INVENTION
[0026] Hereinafter, an embodiment of the invention will be
described with reference to the drawings. FIG. 1 is a
cross-sectional view of a liquid crystal display device 1 related
to an embodiment of the invention. FIG. 2 is a schematic view of
the rear side of a rear frame 31 covering the rear side of a liquid
crystal panel 10 and a backlight unit 20 included in the liquid
crystal display device 1.
[0027] The liquid crystal display device 1 is a device functioning
as, for example, a television. As shown in FIG. 1, the liquid
crystal display device 1 has the liquid crystal panel 10. The
liquid crystal panel 10 has two transparent substrates facing each
other. One substrate (TFT substrate) 10a of the substrates has
plural TFTs (Thin Film Transistors) formed thereon. The TFT
substrate 10a has plural scanning lines and plural signal lines
formed thereon in a matrix form. A gate voltage for turning on/off
the TFT is applied to the scanning line. An image signal
representing a gray-scale value of each pixel is applied to the
signal line. The other substrate (color filter substrate) 10b has
color filters formed thereon. Liquid crystal 10c is sealed between
the TFT substrate 10a and the color filter substrate 10b.
[0028] As shown in FIG. 1, the liquid crystal display device 1 has
the backlight unit 20 disposed on the rear side of the liquid
crystal panel 10 and radiating light toward the rear face of the
liquid crystal panel 10. The backlight unit 20 of this example has
a light source at the edges thereof. The backlight unit 20 has
plural LEDs (Light Emitting Diodes) 21 as a light source. In this
example, the plural LEDs 21 are disposed along the lower and upper
edges of the backlight unit 20. Particularly, the backlight unit 20
has a light guide plate 22, a circuit board 21a disposed along the
lower side of the light guide plate 22, and a circuit board (not
shown) disposed along the upper side of the light guide plate 22.
The LEDs 21 are mounted on the circuit board 21a and face the lower
face of the light guide plate 22. A reflector 23 is disposed on the
rear side of the light guide plate 22. Light of the LEDs 21 emitted
toward the light guide plate 22 is reflected forward by the
reflector 23 while travelling within the light guide plate 22 and
radiated to the rear face of the liquid crystal panel 10. On the
front face of the light guide plate 22, plural optical sheets 25
are disposed. The light source of the backlight unit 20 is not
limited to LED. For example, a cold-cathode tube may be provided as
a light source. Moreover, the light source may be disposed only on
one of the lower and upper sides of the light guide plate 22.
[0029] As shown in FIG. 1, the liquid crystal display device 1 has
a heat discharging plate 24 made of metal. The heat discharging
plate 24 is disposed along the edge of the backlight unit 20 to
absorb heat from the LEDs 21, thereby preventing the heat from
concentrating on the vicinity of the LEDs 21. The heat discharging
plate 24 of this example has a lower plate portion 24a fixed to the
lower face of the circuit board 21a and a rear plate portion 24b
bending at the edge of the lower plate portion 24a and facing the
rear face (particularly the rear face of the light guide plate 22)
of the backlight unit 20. The lower plate portion 24a and the rear
plate portion 24b are integrally formed. The heat discharging plate
24 has substantially the same length as the width of the backlight
unit 20 in the horizontal direction (direction indicated by X1-X2
in FIG. 2). The heat of the LEDs 21 is easily conducted to a
temperature sensor 41 described later through the heat discharging
plate 24.
[0030] As shown in FIG. 1, the liquid crystal display device 1
further has the rear frame 31 made of metal. The rear frame 31 is a
plate-like member and covers the rear side of the backlight unit
20. The rear frame 31 has a rear plate portion 31b facing the rear
face (particularly the rear face of the light guide plate 22) of
the backlight unit 20 and a lower plate portion 31a formed at the
edge of the rear plate portion 31b. The lower plate portion 31a is
disposed along the lower face of the circuit board 21a. In this
example, the lower plate portion 24a of the heat discharging plate
24 is located between the lower plate portion 31a and the circuit
board 21a. The rear plate portion 24b of the heat discharging plate
24 is located between the lowermost portion of the rear plate
portion 31b and the light guide plate 22. Therefore, the heat of
the LEDs 21 is easily conducted to the lowermost portion of the
rear frame 31 through the heat discharging plate 24.
[0031] As shown in FIGS. 1 and 2, circuit boards 12A and 12B are
fixed to the rear frame 31. The circuit boards 12A and 12B are
fixed to the lowermost portion of the rear frame 31 and located
along the lower edge of the backlight unit 20. With this
configuration, the heat of the LEDs 21 is easily conducted to the
circuit boards 12A and 12B. In this example as shown in FIG. 1, the
rear plate portion 24b of the heat discharging plate 24 is located
between the backlight unit 20 and the circuit boards 12A and 12B.
With this configuration, the heat of the LEDs 21 is further easily
conducted to the circuit boards 12A and 12B. The rear plate portion
24b extends upward further than the upper edge of the circuit
boards 12A and 12B. With this configuration, the heat of the LEDs
21 is easily conducted to the wide range of the circuit boards 12A
and 12B.
[0032] The liquid crystal display device 1 includes at least one
temperature sensor used for temperature estimation of the liquid
crystal panel 10. The liquid crystal display device 1 of this
example includes one temperature sensor 41 as shown in FIGS. 1 and
2. The temperature sensor 41 is attached to the circuit board
12A.
[0033] As shown in FIG. 2, the liquid crystal display device 1
further has a TFT control circuit board 13, a power circuit board
14, and an application circuit board 15. In this example, all of
the boards 13, 14, and 15 are fixed to the rear frame 31. In this
example, a controller 2 and a memory 3, which will be described
later, are mounted on the TFT control circuit board 13. On the
application circuit board 15, a circuit functioning as an interface
to external equipment is mounted. On the power circuit board 14, a
power supply circuit which supplies driving power to each of the
circuits included in the liquid crystal display device 1 is
mounted.
[0034] The circuit board 12A to which the temperature sensor 41 is
attached and the circuit board 12B which is disposed side by side
with the circuit board 12A in the horizontal direction are circuit
boards closest to the LEDs 21, among the plural circuit boards of
the liquid crystal display device 1. In this example, the TFT
control circuit board 13 is located at the central part of the rear
frame 31 in the horizontal direction and located upper to the
circuit boards 12A and 12B. The power circuit board 14 and the
application circuit board 15 are disposed on the left and right
sides of the TFT control circuit board 13 and located upper to the
circuit boards 12A and 12B, respectively. Since the circuit board
12A of the two circuit boards 12A and 12B is located away from the
power circuit board 14, the circuit board 12A is insusceptible to
heat from the power circuit board 14. On the other hand, since the
circuit board 12B is located away from the application circuit
board 15, the circuit board 12B is insusceptible to heat from the
application circuit board 15. When only one temperature sensor is
used, one circuit board which can more properly detect a
temperature may be selected from the circuit boards 12A and 12B. In
the embodiment, in view of the influence of heat from the power
circuit board 14, the temperature sensor 41 is disposed on the
circuit board 12A. Therefore, an output value of the temperature
sensor 41 is insusceptible to heat from the power circuit board
14.
[0035] A later-described process based on the output value of the
temperature sensor 41 is executed in the controller 2 mounted on
the TFT control circuit board 13. As shown in FIG. 2, the circuit
boards 12A and 12B and the application circuit board 15 are
connected to the TFT control circuit board 13 through FPCs
(Flexible Printed Circuits) 16 and 17. As described above, the
temperature sensor 41 is attached to the circuit board 12A.
Therefore, it is unnecessary to provide dedicated wiring for
inputting an output signal of the temperature sensor 41 to the
controller 2. That is, the output signal of the temperature sensor
41 is input to the controller 2 through the FPC 16.
[0036] As described above, the circuit board 12A is so disposed
that the heat of the LEDs 21 is easily conducted to the circuit
board 12A. Therefore, the heat of the LEDs 21 is properly reflected
in the output value of the temperature sensor 41. The temperature
of the liquid crystal panel 10 is susceptible to the heat of the
LEDs 21. Due to such an arrangement of the temperature sensor 41
and the circuit board 12A, the accuracy of temperature estimation
of the liquid crystal panel 10 using the temperature sensor 41 can
be increased.
[0037] As shown in FIG. 1, the liquid crystal display device 1
includes a plate-like board cover 33. The board cover 33 covers the
circuit boards 12A and 12B. The temperature sensor 41 is located
inside the board cover 33. Therefore, the output value of the
temperature sensor 41 is insusceptible to outside air temperature.
As a result, the accuracy of temperature estimation of the liquid
crystal panel 10 using the temperature sensor 41 can be increased.
The edge of the board cover 33 protrudes toward the rear frame 31.
With this configuration, it is further difficult for outside air to
enter the inside of the board cover 33.
[0038] As shown in FIG. 1, the circuit board 12A is fixed to the
rear frame 31 with screws 32. FIG. 3 is a schematic plan view of
the circuit board 12A illustrating positions of the screws 32 and
temperature sensor 41. In the drawing, the board cover 33 is not
illustrated. As shown in FIG. 3, the circuit board 12A is fixed to
the rear frame 31 with the plural screws 32. The screws 32 are made
of metal, and part of heat of the rear frame 31 is conducted to the
circuit board 12A through the screws 32. The position of the
temperature sensor 41 is close to one of the screws 32. Therefore,
heat from the LEDs 21 can be properly reflected in the output value
of the temperature sensor 41. As shown in FIG. 1, the screw 32 of
this example is inserted from the outside of the board cover 33 and
fixes not only the circuit board 12A but also the board cover 33 to
the rear frame 31. The temperature sensor 41 is interposed between
the circuit board 12A and the board cover 33.
[0039] As shown in FIG. 1, the circuit boards 12A and 12B are
connected to the lower edge of the liquid crystal panel 10 through
an FPC 12a. An IC chip 12b is mounted on the FPC 12a. The IC chip
12b is located away from the temperature sensor 41. Therefore, the
temperature sensor 41 is less exposed to heat from the IC chip 12b.
In this example, the IC chip 12b is located outside the board cover
33. Therefore, the temperature sensor 41 is much less exposed to
heat from the IC chip 12b. The IC chip 12b functions as a signal
line drive circuit 4 described later. The circuit boards 12A and
12B are each generally referred to as a source board and each
function as a junction circuit board connecting the signal line
drive circuit 4 with the controller 2. The IC chip 12b applies a
voltage according to a gray-scale value to a source of TFT.
[0040] As shown in FIG. 1, the liquid crystal display device 1 has
a front cover 51 covering the outer periphery of the liquid crystal
panel 10 and a rear cover 52 covering the rear side of the rear
frame 31 and constituting the rear face of the liquid crystal
display device 1. Further, the liquid crystal display device 1 has
a middle frame 53.
[0041] FIG. 4 is a block diagram schematically showing circuits
included in the liquid crystal display device 1. As shown in the
drawing, the liquid crystal display device 1 has the controller 2,
the memory 3, the signal line drive circuit 4, a scanning line
drive circuit 5, and a backlight drive circuit 6.
[0042] An input image signal received by a not-shown tuner or
antenna and an input image signal generated by another device such
as a video player are input to the controller 2. The controller 2
includes a CPU (Central Processing Unit), is connected to the
memory 3 such as a ROM (Read Only Memory) or RAM (Random Access
Memory), and executes programs stored in the memory 3. For example,
the controller 2 generates, based on the input image signal, an
output image signal representing a gray-scale value of each pixel
and outputs the image signal to the signal line drive circuit 4.
Moreover, the controller 2 generates, based on the input image
signal, a timing signal for synchronizing the signal line drive
circuit 4 with the scanning line drive circuit 5 and outputs the
timing signal to each of the drive circuits. The temperature sensor
41 is connected to the controller 2. The controller 2 executes,
based on the output value of the temperature sensor 41, a process
for estimating the temperature of the liquid crystal panel 10. The
process executed by the controller 2 will be described later in
detail.
[0043] The scanning line drive circuit 5 is connected to the
scanning lines formed on the TFT substrate 10a and applies a gate
voltage in sequence to the plural scanning lines in time with the
timing signal input from the controller 2. The scanning line drive
circuit 5 is mounted on a not-shown board disposed on, for example,
the left or right side of the liquid crystal panel 10.
[0044] The signal line drive circuit 4 is connected to the signal
lines formed on the TFT substrate 10a and applies to each of the
signal lines a voltage according to the output image signal from
the controller 2 in time with the timing of applying the gate
voltage. The signal line drive circuit 4 is mounted on the FPC 12a
in the embodiment but may be mounted on, for example, the circuit
board 12A or 12B, or the TFT substrate 10a.
[0045] The backlight drive circuit 6 supplies its driving power to
the LEDs 21 based on a signal input from the controller 2. The
controller 2 has, as drive modes of the backlight unit 20, plural
drive modes depending on which the luminance of the LEDs 21 varies.
For example, the controller 2 has a high luminance mode in which
the LEDs 21 are driven at high luminance, a low luminance mode in
which the LEDs 21 are driven at low luminance, and a middle
luminance mode in which the LEDs 21 are driven at middle luminance.
The backlight drive circuit 6 receives a signal representing a
drive mode from the controller 2 and supplies the LEDs 21 with
driving power corresponding to the drive mode. The backlight drive
circuit 6 is mounted also on a not-shown board.
[0046] FIG. 5 is a block diagram showing functions of the
controller 2. As shown in the drawing, the controller 2 includes,
as its functions, a sensor output acquiring section 2a, a
temperature estimating section 2b, and a correction processing
section 2c. The sensor output acquiring section 2a acquires the
output value of the temperature sensor 41 with a predetermined
sampling period (for example, 10 seconds). When output from the
temperature sensor 41 is an output signal in the form of analog,
the output is input as a digital signal to the controller 2 through
a not-shown A/D conversion circuit. The sensor output acquiring
section 2a acquires a value represented by the digital signal as
the output value of the temperature sensor 41. On the other hand,
when the output from the temperature sensor 41 is an output signal
in the form of digital, the sensor output acquiring section 2a
acquires a value represented by the digital signal as it is as the
output value of the temperature sensor 41.
[0047] As described above, the temperature sensor 41 is attached at
a position where the temperature sensor is susceptible to heat from
the LEDs 21. Moreover, the temperature of the liquid crystal panel
10 is strongly affected by heat from the LEDs 21. Therefore, there
is a correlation between the output value of the temperature sensor
and the temperature of the liquid crystal panel 10. The temperature
estimating section 2b estimates the temperature of the liquid
crystal panel 10 based on the output value acquired in the sensor
output acquiring section 2a.
[0048] As shown in FIG. 4, plural areas A1 to A25 whose number is
larger than that of the temperature sensor 41 are defined on the
liquid crystal panel 10. That is, the total area of the liquid
crystal panel 10 is divided virtually into the plural areas A1 to
A25. In the example shown in FIG. 4, the liquid crystal panel 10 is
divided into five parts in each of the vertical and horizontal
directions and has 25 areas in total. The number of areas defined
on the liquid crystal panel 10 is not limited to that and may be
appropriately changed according to the size of the liquid crystal
panel 10.
[0049] FIG. 6 is a diagram showing an example of temporal change in
output value of the temperature sensor 41 and temporal change in
actual temperature of each area. In the drawing, temperatures
(measured values) of the areas A3, A13, and A15 are shown as
examples. Moreover in the drawing, the backlight unit 20 is driven
in the high luminance mode until t1, driven in the low luminance
mode from t1 to t2, and driven in the middle luminance mode after
t2. As shown in the drawing, the temperature of any of the areas
changes according to the switching of the drive mode of the
backlight unit 20. In the liquid crystal display device 1, the LEDs
21 are disposed at the edges of the backlight unit 20. It is found
from FIG. 6 that temperature distribution occurs at each of the
areas in the liquid crystal panel 10. As shown in FIG. 1, the
temperature sensor 41 is disposed at a position where the
temperature of the LEDs 21 is easily detected. Therefore as shown
in FIG. 6, there is a correlation between the output value of the
temperature sensor 41 and the temperature of each of the areas. In
the example described herein, a temperature (temperature of the
area A3 in the drawing) of an area close to the position (the upper
and lower edges of the backlight unit 20 in this example) of the
LEDs 21 of the liquid crystal panel 10 is higher than temperatures
of the other areas (the area A13 and the area A15 in the drawing).
Moreover, the liquid crystal panel 10 has, on the rear side of the
right-side and left-side portions of the liquid crystal panel 10,
small number of components serving as a heat source such as a
circuit board. Therefore, a temperature of the right-side or
left-side portion of the liquid crystal panel 10 (temperature of
the area A15 in the example of the drawing) is lower than a
temperature (temperature of the area A13 in the drawing) of an area
at the center of the panel. A change in temperature of the LEDs 21
is dominant over the temperature of each area of the liquid crystal
panel 10. Therefore, the tendency of change in temperature of the
areas A1 to A25 can be grasped from the output value of the
temperature sensor 41 placed at a position where the temperature
sensor is susceptible to the temperature of the LEDs 21.
[0050] In the embodiment, the memory 3 has temperature relation
information stored therein in advance and representing a relation
between the output value of the temperature sensor 41 and the
temperature of each of the areas A1 to A25. The temperature
estimating section 2b estimates the temperature of each of the
plural areas A1 to A25 based on the temperature relation
information and the output value acquired in the sensor output
acquiring section 2a.
[0051] The temperature estimating section 2b uses plural relation
formulas (hereinafter, temperature relation formula(s)) defined by
the temperature relation information to estimate the temperatures
of the areas A1 to A25. The plural temperature relation formulas
represent the relations between the output value of the temperature
sensor 41 and the temperatures of the areas A1 to A25,
respectively. That is, the plural temperature relation formulas
respectively correspond to the areas A1 to A25, and a relation
between a temperature of one area and an output value of the
temperature sensor 41 is represented by a temperature relation
formula corresponding to the area.
[0052] In this example, plural coefficients respectively associated
with the areas A1 to A25 are stored in the memory 3. A temperature
relation formula for one area is defined by coefficients
corresponding to the area. Moreover in this example, a fundamental
relation formula to which the plural coefficients associated with
each of the areas A1 to A25 can be applied selectively is stored in
the memory 3. The fundamental relation formula is a formula serving
as a source of the temperature relation formula for each of the
areas, and coefficients corresponding to each area are applied to
the fundamental relation formula, whereby a temperature relation
formula for a relevant area can be obtained.
[0053] The fundamental relation formula is expressed by, for
example, Expression (1) below.
T=K.times.Td(i)+R.times.F(Td(i))+OFS (1)
T is a temperature estimated for any of the areas. Td(i) is a
latest output value acquired by the sensor output acquiring section
2a. K, R and OFS are constants. Specifically, K and R are
coefficients, and OFS is an offset value. When a temperature of
each area is calculated, specific constants corresponding to the
area are applied. For example, when the temperature of the area A1
is calculated, constants (K.sub.A1, R.sub.A1, OFS.sub.A1)
associated with the area A1 are applied to the constants K, R, and
OFS in the above expression (1). A function F is a filter function
which outputs a value reflecting an output value acquired before
the latest output value.
[0054] The function F is, for example, an IIR filter (Infinite
Impulse Response Filter) and expressed by, for example, Expression
(2) below.
F(Td(i))=Td(i).times.(1-H)+F(Td(i-1)).times.H (2)
Td(i-1) is an output value acquired at the previous process by the
sensor output acquiring section 2a. H is a filter coefficient. When
a temperature of each area is calculated, a specific coefficient
corresponding to the area is applied. For example, when the
temperature of the area A1 is calculated, a coefficient (H.sub.A1)
associated with the area A1 is applied to the coefficient H. Since
the fundamental relation formula includes the filter function, a
value output by the temperature relation formula is based not only
on the latest output value of the temperature sensor 41 but also on
at least the output value acquired at the previous process. This
makes it possible to compensate a lag between a change of the
output value of the temperature sensor 41 and a change of the
actual temperature of the liquid crystal display panel 10. Further,
this makes it possible to prevent a temperature calculated by the
temperature estimating section 2b from following an instantaneous
change or noise in output value acquired by the sensor output
acquiring section 2a. The function F is not limited to the IIR
filter. The function F may be, for example, a FIR filter (Finite
Impulse Response Filter).
[0055] As shown by Expression (1), the temperature relation formula
defined by the fundamental relation formula and the constants
associated with each of the areas is a first order filter function
for the output value of the temperature sensor 41. Therefore, the
processing load of temperature estimation can be reduced. The
temperature relation formula is not limited to that described
above. For example, the temperature relation formula may be a
second order filter function or third order filter function for the
output value of the temperature sensor 41.
[0056] As described above, the temperature relation formula is
defined by the plural constants (hereinafter referred to as
constant group) associated with the areas A1 to A25. For example,
the temperature relation formula for the area A1 is defined by a
constant group (K.sub.A1, R.sub.A1, OFS.sub.A1, and H.sub.A1). In
this example, a table (hereinafter, constant table) which
associates areas with constant groups, respectively, shown in FIG.
7, is stored in the memory 3.
[0057] In this embodiment where such temperature relation
information is stored in the memory 3, the temperature estimating
section 2b executes the following process for estimating the
temperature of each area. In the process for estimating the
temperature of an area Am (m=1, 2, . . . , and 25 in this example),
the temperature estimating section 2b first refers to the constant
table to select a constant group corresponding to the area Am.
Then, the temperature estimating section 2b uses a fundamental
relation formula to which the selected constant group is applied,
that is, a temperature relation formula representing a relation
between the output value of the temperature sensor 41 and the
temperature of the area Am to calculate the temperature of the area
Am from the output value acquired by the sensor output acquiring
section 2a. The temperature estimating section 2b executes the
process described above for each area to estimate the temperatures
of all the areas A1 to A25. The temperature estimating section 2b
executes the process described above with a predetermined period
(for example, the same period as the sampling period of the sensor
output acquiring section 2a) to calculate the temperatures of the
areas A1 to A25.
[0058] The process executed by the temperature estimating section
2b and the information stored in the memory 3 is not limited to
that described above. For example, plural temperature relation
formulas respectively associated with the areas A1 to A25 may be
previously stored in the memory 3 as temperature relation
information. Moreover, plural tables representing temperatures of
the areas A1 to A25 may be stored in the memory 3 respectively in
association with plural output values which can be output by the
temperature sensor 41. In this case, the temperature estimating
section 2b reads from the memory 3 a table corresponding to an
output value acquired in the sensor output acquiring section 2a.
Then, the temperature estimating section 2b defines temperatures
which are set in the read table as estimated temperatures of the
areas A1 to A25.
[0059] The relation between the output value of the temperature
sensor 41 and the temperature of the liquid crystal panel 10 varies
depending on an elapsed time since the start of driving (when the
power is turned on) of the liquid crystal display device 1. After a
sufficient time has elapsed since the start of driving, there is
the correlation, illustrated in FIG. 6, between the temperature of
each of the areas and the output value of the temperature sensor
41. However, under the situation where the liquid crystal display
device 1 is not driven, both of a temperature in the vicinity of
the temperature sensor 41 and the temperature of each area depend
on the temperature of an environment where the liquid crystal
display device 1 is placed, and are substantially equal to each
other. Therefore, until a sufficient time has elapsed since the
start of driving of the liquid crystal display device 1, the
temperature of each of the areas and the output value of the
temperature sensor 41 sometimes do not have the relation
represented by the temperature relation formula described
above.
[0060] FIG. 8 is a diagram showing an example of temporal changes
in output value of the temperature sensor 41 and in temperature of
each area. In the drawing, the changes since the start of driving
of the liquid crystal display device 1 are shown. Moreover in the
drawing, temperatures of the areas A3, A13, and A15 are shown as
examples. In the case shown in the drawing, the backlight unit 20
is driven in the high luminance mode from the start of driving when
the power is turned on to t1, driven in the low luminance mode from
t1 to t2, and driven in the middle luminance mode after t2. As
shown in the drawing, after a sufficient time has elapsed (that is,
in a steady-state period shown in the drawing) since the start of
driving of the liquid crystal display device 1, there is a high
correlation represented by the temperature relation formula
described above. However, until a sufficient time has elapsed (that
is, in a transient period shown in the drawing) since the start of
driving of the liquid crystal display device 1, a relation between
the temperature of each of the areas and the output value of the
temperature sensor 41 is not similar to that of the steady-state
period, and a difference between the temperature of each of the
areas and the output value of the temperature sensor 41 is
gradually increased over time.
[0061] Therefore, the temperature estimating section 2b may
determine, based on information changing according to the elapsed
time since the start of driving of the liquid crystal display
device 1, whether or not a present time falls to the steady-state
period. Then, the temperature estimating section 2b may estimate
the temperatures of the areas A1 to A25 by a process different
depending on whether or not the present time falls to the
steady-state period.
[0062] The process for determining whether or not the present time
falls to the steady-state period is executed as follows, for
example. The temperature estimating section 2b initiates timing at
the start of driving of the liquid crystal display device 1 and
determines, based on the elapsed time since the start of driving,
whether or not the present time has reached the steady-state
period. That is, the temperature estimating section 2b determines
that the present time has reached the steady-state period when the
elapsed time since the start of driving exceeds a predetermined
time. Moreover as shown in FIG. 8, the output value of the
temperature sensor 41 abruptly changes immediately after the start
of driving of the liquid crystal display device 1. Therefore, the
temperature estimating section 2b may determine, based on the rate
of change in output value of the temperature sensor 41, whether or
not the present time falls to the steady-state period. For example,
the temperature estimating section 2b may determine, based on
differences each defined as a difference between two output values
acquired with a predetermined period, whether or not the present
time falls to the steady-state period. If the difference is smaller
than a threshold value, the present time may be determined as
falling to the steady-state period.
[0063] If the present time falls to the steady-state period, the
temperature estimating section 2b uses the constant group and
fundamental relation formula described above to estimate the
temperature of each area. On the other hand, if the present time
does not fall to the steady-state period, that is, if the present
time falls to the transient period, the temperature estimating
section 2b uses, for example, a constant group different from the
constant group described above and/or a relation formula different
from the fundamental relation formula described above to estimate
the temperature of each area. In this case, the memory 3 has
temperature relation information stored therein which represent a
relation between the output value of the temperature sensor 41 and
the temperature of each area in the transient period and which is
different from the temperature relation information described above
to be used in the steady-state period. Also the temperature
relation information in the transient period is composed of, for
example, a fundamental relation formula and a constant group
associated with each area. As another example, in the transient
period, the temperature estimating section 2b may correct a value
calculated using the constant group and fundamental relation
formula described above and define the corrected value as the
temperature of each area in the transient period. In this case, the
temperature estimating section 2b may correct the value obtained
from the constant group and the fundamental relation formula
described above used in the steady-state period based on, for
example, the rate of change in output value of the temperature
sensor 41.
[0064] FIGS. 9A and 9B are diagrams each showing a change in
temperature of each area in the transient period. In the case shown
in those diagrams, changes in temperature of the areas A3, A13, and
A15 are shown as examples. FIG. 9A shows an example of change in
the case where the driving of the liquid crystal display device 1
is resumed after along time has elapsed since the end of previous
driving (when the power is turned off). FIG. 9B shows an example of
change in the case where the driving is resumed without a
sufficient time interval since the end of previous driving. When a
long time has elapsed since the end of driving, a temperature in
the vicinity of the temperature sensor 41 and the temperature of
each area are equal to each other. Therefore as shown in FIG. 9A,
at the start of driving after a long time has elapsed, temperatures
of all areas are equal to each other. In a case where only a short
time has elapsed, however, differences in temperature among the
areas are not eliminated. Therefore, when the driving is resumed
without a sufficient time interval after the end of previous
driving, the differences in temperature among the areas already
exist at the start of driving of the liquid crystal display device
1 as shown in FIG. 9B.
[0065] Therefore, the temperature estimating section 2b may change,
based on information changing according to the elapsed time since
the end of previous driving, the constant group and/or fundamental
relation formula used in the transient period. This process can be
executed, for example, as follows.
[0066] The temperature estimating section 2b stores, at the end of
driving of the liquid crystal display device 1, the output value of
the temperature sensor 41 in the memory 3. Thereafter, when the
driving is resumed, the temperature estimating section 2b may
determine, based on a difference between the output value of the
temperature sensor 41 acquired at the start of driving and the
output value stored in the memory 3 at the end of previous driving,
whether or not a sufficient time has elapsed since the end of
previous driving. For example, if the difference between the output
value of the temperature sensor 41 acquired at the start of driving
and the output value stored in the memory 3 at the end of previous
driving is larger than a threshold value, the temperature
estimating section 2b determines that a sufficient time has elapsed
since the end of previous driving. The temperature estimating
section 2b may change the constant group and/or fundamental
relation formula used in the transient period after the start of
driving depending on whether or not a sufficient time has elapsed
since the end of previous driving.
[0067] The correction processing section 2c corrects various kinds
of parameters related to an image to be displayed on the liquid
crystal panel 10. The correction processing section 2c calculates
parameters related to an image to be displayed in an area Am of the
plural areas A1 to A25 based on a temperature estimated for the
area Am. The parameters are, for example, gray-scale values of
pixels formed on the TFT substrate 10a or voltages to be applied to
a common electrode (not shown) formed on the TFT substrate 10a or
the color filter substrate 10b. That is, in one example, the
correction processing section 2c corrects, based on the estimated
temperature, a gray-scale value calculated from an input image
signal and outputs a signal corresponding to the corrected
gray-scale value as an output image signal (such a correction is
executed as for example, a correction for eliminating crosstalk
between two successive frames). In another example, the correction
processing section 2c corrects the voltages to be applied to the
plural electrodes provided at the edge of the common electrode
based on temperatures of the areas A1 to A25 (Vcom correction).
[0068] Herein, the correction processing section 2c which corrects
gray-scale values will be described as an example. The correction
processing section 2c corrects the gray-scale values of pixels
formed in an area Am based on a temperature estimated for the area
Am. As shown in FIG. 5, the correction processing section 2c
includes a gray-scale value table selecting section 2d and a
gray-scale value calculating section 2e.
[0069] The gray-scale value calculating section 2e calculates,
based on a gray-scale value of a previous frame and a gray-scale
value (gray-scale value before correction) according to an input
image signal of a next frame, a gray-scale value (gray-scale value
after correction) of the next frame and outputs a signal
corresponding to the calculated gray-scale value as an output image
signal. The memory 3 has a table stored therein in which candidates
for gray-scale values calculated by the gray-scale value
calculating section 2e. In the gray-scale value table, the
gray-scale value of the next frame is set in association with the
gray-scale value of the previous frame and the gray-scale value
according to the input image signal of the next frame. The memory 3
has plural gray-scale value tables stored therein which are in
association with temperatures. The gray-scale value table selecting
section 2d selects the gray-scale value table based on a
temperature calculated in the temperature estimating section 2b for
each area. That is, the gray-scale value table selecting section 2d
selects the gray-scale value table for each of the plural areas A1
to A25.
[0070] FIG. 10 is a diagram showing an example of a gray-scale
value table. In the table in the diagram, gray-scale values
according to the input image signals of the next frame are shown in
the top row. Gray-scale values set in the previous frame are shown
in the leftmost column. In the memory 3, such plural gray-scale
value tables are stored in association with temperatures (refer to
FIG. 5).
[0071] When the temperature estimating section 2b calculates a
temperature for each of the areas A1 to A25, the gray-scale value
table selecting section 2d selects, based on each of the
temperatures, the gray-scale value table for each of the plural
areas A1 to A25. Then as shown in FIG. 5, the gray-scale value
table selecting section 2d stores the selected gray-scale value
tables, in association with the areas A1 to A25, in a memory area
defined previously within the memory 3. That is, after selecting
the gray-scale value table based on the temperature of an area Am,
the gray-scale value table selecting section 2d stores the selected
gray-scale value table in the memory 3 in association with the area
Am. When a new temperature is calculated in the temperature
estimating section 2b, the gray-scale value table selecting section
2d selects the gray-scale value table based on the new temperature
and updates the gray-scale value table which has been already
stored to the newly selected gray-scale value table.
[0072] The gray-scale value calculating section 2e calculates the
gray-scale values of pixels in each area with reference to the
gray-scale value table associated with a relevant area. That is,
when calculating the gray-scale value of one pixel, the gray-scale
value calculating section 2e selects a gray-scale value table
associated with an area including the pixel. Then, the gray-scale
value calculating section 2e refers to the selected gray-scale
value table to calculate a gray-scale value corresponding to a
gray-scale value set for the pixel in the previous frame and a
gray-scale value of the pixel according to the input image signal
for the next frame. The gray-scale value calculating section 2e
executes the process described above for all pixels in one
frame.
[0073] In the gray-scale value table, all values from a minimum
gray-scale value (0 in FIG. 10) to a maximum gray-scale value (255
in FIG. 10) may be defined as the gray-scale values in the previous
frame and the gray-scale values according to the input image
signals for the next frame. Moreover, like the gray-scale value
table shown in FIG. 10, the gray-scale values in the previous frame
and the gray-scale values according to the input image signals for
the next frame may be set stepwise from the minimum gray-scale
value to the maximum gray-scale value. That is, a difference larger
than 1 may be provided between two successive gray-scale values. In
using the gray-scale value table in FIG. 10, when a gray-scale
value in the previous frame or a gray-scale value according to the
input image signal for the next frame is a value between two
successive gray-scale values, the gray-scale value calculating
section 2e executes an interpolation process which interpolates a
value between two successive gray-scale values.
[0074] A method for obtaining constants used for the temperature
estimation of the areas A1 to A25 in manufacturing process of the
liquid crystal display device 1 will be described. FIG. 11 is a
diagram for explaining the arrangement of temperature detectors 51
used in obtaining the constants. First, the temperature detector 51
(for example, a thermocouple) is disposed at plural positions (25
positions in this example) on the surface of the liquid crystal
panel 10. For example as shown in FIG. 11, one temperature detector
51 is provided in each of the areas A1 to A25. Then, the liquid
crystal display device 1 is driven while changing the drive mode of
the backlight unit 20 in plural temperature environments. For
example, the drive mode (the high luminance mode, the middle
luminance mode, and the low luminance mode) of the backlight unit
20 is changed in order in an environment of 0 degree, and
thereafter the drive mode of the backlight unit 20 is changed in
another temperature environment. At that time, an actual
temperature is measured by the temperature detector 51 provided on
the liquid crystal panel 10 at a fixed time interval (for example,
an interval of 10 seconds), and the output value of the temperature
sensor 41 is acquired at the fixed time interval. FIG. 12
illustrates temporal changes in output value of the temperature
sensor 41 and in measured temperature obtained by the temperature
detector 51. With the temperature measurement described above, as
shown in FIG. 12, a number of measured temperatures for each
position (temperature measurement position) at which a temperature
detector 51 is attached and the output values of the temperature
sensor 41 respectively corresponding to the measured temperatures
are obtained. Then, an approximate expression between a measured
temperature and the output value of the temperature sensor 41 is
obtained. When one temperature detector 51 is provided in each
area, that is, when one temperature measurement position
corresponds to one area, an approximate expression for an area Am
including constant K.sub.Am, R.sub.Am, H.sub.Am, and OFS.sub.Am is
obtained from the output value of the temperature sensor 41 and a
measured temperature at a temperature measurement position provided
in the area Am. An estimated temperature corresponding to a
temperature measurement position is deemed, in the process of the
temperature estimating section 2b, as an estimated temperature of
the entire of an area including the temperature measurement
position. Specifically, the estimated temperature of an area Am is
represented by the estimated temperature at the temperature
measurement position provided in the area Am. The derivation of the
approximate expression can be carried out by, for example, the
method of least squares. That is, a value which minimizes the sum
of the squares of the difference between the temperature
(temperature obtained from Expression (1)) of an area Am based on
the output value of the temperature sensor 41 and the measured
temperature of the area Am is defined as constants for the area Am.
In the case where the constants are derived in this manner, a
temperature estimation error can be reduced when the drive mode of
the backlight unit 20 is changed.
[0075] The provision of temperature measurement positions is not
limited to that described above. For example, plural temperature
detectors 51 may be provided in each area. That is, plural
temperature measurement positions may be associated with one area.
In the example shown in FIG. 13, a temperature measurement position
is provided at the corners of each area, and four temperature
measurement positions are associated with one area. When the
temperature measurement positions are provided in this manner, an
actual temperature of one area Am is calculated from measured
temperatures at plural temperature measurement positions associated
with the area Am. For example, the average value of the measured
temperatures at the plural temperature measurement positions is
used as the actual temperature of the area Am. Then, for the area
Am, the output value of the temperature sensor 41 and the
calculated temperature of the area Am are used to obtain an
approximate expression including the coefficients K.sub.Am,
R.sub.Am, H.sub.Am, and OFS.sub.Am.
[0076] As described above, the temperature relation information
representing the relation between the output value of the
temperature sensor 41 and the temperature of each of the plural
areas A1 to A25 defined on the liquid crystal panel 10 is stored in
the memory 3 in advance. The controller 2 acquires the output value
of the temperature sensor 41 and estimates the temperature of each
of the areas A1 to A25 based on the temperature relation
information and the acquired output value. Therefore, it is
possible to obtain the temperature of each of the plural areas A1
to A25 defined on the liquid crystal panel 10 with a small number
of temperature sensors.
[0077] The invention is not limited to the liquid crystal display
device 1 described above but can be modified variously.
[0078] For example, in the liquid crystal display device 1
described above, one temperature sensor 41 is provided. However,
many more temperature sensors may be provided in the liquid crystal
display device 1.
[0079] FIG. 14 is a rear side view of the rear frame 31 included in
a liquid crystal display device of this example. In this drawing,
the same reference and numeral signs are assigned to the same
portions as those described so far. Hereinafter, only the
differences from the liquid crystal display device 1 described so
far will be described, and the matters not described herein are
similar to those of the liquid crystal display device 1.
[0080] The liquid crystal display device shown in FIG. 14 includes
plural temperature sensors 41, 42, 43, and 44 which are disposed
away from each other. Also in this example, the number of areas
defined on the liquid crystal panel 10 is larger than the number of
temperature sensors. The temperature sensor 42 is attached to the
circuit board 12B attached at the lower edge of the rear frame 31.
The temperature sensor 41 and the temperature sensor 42 are located
away from each other in a direction along the lower edge of the
rear frame 31. The temperature sensor 43 is attached to the TFT
control circuit board 13. The temperature sensor 44 is attached to
the application circuit board 15. Output signals of the sensors 41
to 44 are input to the controller 2 directly or indirectly. In the
example of the drawing, the outputs of the temperature sensors 41,
42, and 43 are directly input to the controller 2, while the output
of the temperature sensor 44 is input to the controller 2 through
an IC chip 15a mounted on the application circuit board 15. In the
liquid crystal display device, many more temperature sensors may be
provided. For example, plural (for example, three) temperature
sensors located away from each other so as to surround the
controller 2 may be provided on the TFT control circuit board
13.
[0081] In this example, temperature relation information
representing a relation between the output values of the plural
temperature sensors 41 to 44 and the temperature of each of the
plural areas A1 to A25 are stored in the memory 3 in advance. For
example, a fundamental relation formula serving as a source of
temperature relation formulas for the areas A1 to A25 and plural
constant groups respectively associated with the areas A1 to A25
are stored in the memory 3 as the temperature relation information.
The temperature estimating section 2b uses the temperature relation
formula defined by the constant group corresponding to each area to
calculate the temperature of a relevant area based on the output
values of the plural temperature sensors 41 to 44.
[0082] The fundamental relation formula of this example is
expressed by, for example, Expression (3).
T=K1.times.Td1(i)+R1.times.F(Td1(i),H1)+K2.times.Td2(i)+R2.times.F(Td2(i-
),H2)+K3.times.Td3(i)+R3.times.F(Td3(i),H3)+K4.times.Td4(i)+R4.times.F(Td4-
(i),H4)+OFS (3)
Td1(i), Td2(i), Td3(i), and Td4(i) are the latest output values of
the temperature sensors 41, 42, 43, and 44, respectively. K1 to K4,
R1 to R4, H1 to H4, and OFS are constants. When the temperature of
each area is calculated, specific constants corresponding to a
relevant area are applied. For example, when the temperature of an
area Am is calculated (m=1, 2, . . . , and 25), constants
(K1.sub.Am to K4.sub.Am, R1.sub.Am to R4.sub.Am, H1.sub.Am to
H4.sub.Am, and OFS.sub.Am) associated with the area Am are applied
to the constants K1 to K4, R1 to R4, H1 to H4, and OFS of
Expression (3). F is a filter function similar to that shown in
Expression (2) and defined by the filter coefficients H1 to H4.
[0083] As shown by Expression (3), the temperature relation formula
of this example is a first order filter function of the output
values of the temperature sensors 41, 42, 43, and 44. Therefore,
the processing load of temperature estimation is reduced. The
temperature relation formula is not limited to that. For example,
the temperature relation formula may be a second order filter
function or a third order filter function of the output value of
any of the temperature sensors.
[0084] The plural constant groups respectively associated with the
areas A1 to A25 and the fundamental relation formula (3) to which
the plural constant groups can be applied selectively are stored in
the memory 3 in advance. The constant groups are also stored in the
memory 3 in association with the areas, similarly to the constant
table described with reference to FIG. 7.
[0085] Even when the temperature relation information described
above is stored in the memory 3, the process executed by the sensor
output acquiring section 2a and the temperature estimating section
2b is similar to the form described above. That is, the sensor
output acquiring section 2a acquires the output values of the
temperature sensors 41, 42, 43, and 44 with a predetermined
sampling period. In the process for estimating the temperature of
an area Am, the temperature estimating section 2b first selects a
constant group corresponding to the area Am from the plural
constant groups. Then, the temperature estimating section 2b uses a
temperature relation formula defined by the selected constant group
and the fundamental relation formula shown by Expression (3) to
calculate the temperature of the area Am from the output values of
the plural temperature sensors 41, 42, 43, and 44. The temperature
estimating section 2b executes the process described above for all
the areas A1 to A25.
[0086] When the plural temperature sensors 41, 42, 43, and 44 are
provided in the liquid crystal display device like this example,
the temperature estimating section 2b may determine, by the
following process, whether or not a sufficient time has elapsed
since the end of previous driving of the liquid crystal display
device, that is, whether or not a present time falls to the
steady-state period.
[0087] If a sufficient time has elapsed since the end of previous
driving of the liquid crystal display device, the output values of
the temperature sensors 41, 42, 43, and 44 become values depending
on environmental temperature and are equal to each other. The
temperature sensors 41, 42, 43, and 44 are different from each
other in attachment position or distance from the LEDs 21. That is,
the temperature sensors 41, 42, 43, and 44 are different from each
other in conductivity of heat of the LEDs 21. Therefore, in the
steady-state period, differences are generated in the output values
of the temperature sensors 41, 42, 43, and 44. Therefore, the
temperature estimating section 2b determines that a present time
falls to the steady-state period if a difference in output value
between any two of the temperature sensors is larger than a
threshold value. That is, the temperature estimating section 2b may
use, as information changing according to the elapsed time since
the start of driving of the liquid crystal display device, the
difference in output value between two temperature sensors. For
example, if a difference between the output value of a temperature
sensor (the temperature sensor 41 or 42 in this example) provided
at a position most susceptible to heat from the LEDs 21 and the
output value of another temperature sensor (the temperature sensor
43 or 44 in this example) located away from the temperature sensor
mentioned before is larger than a threshold value, the temperature
estimating section 2b may determine that the present time falls to
the steady-state period.
[0088] A method for obtaining the constants associated with each of
the areas A1 to A25 in a manufacturing process of the liquid
crystal display device is similar to that described above. That is,
the liquid crystal display device is driven while changing the
drive mode of the backlight unit 20 in plural temperature
environments. At that time, an actual temperature of each of the
areas A1 to A25 of the liquid crystal panel 10 is measured with a
fixed time interval, and the output values of the temperature
sensors 41, 42, 43, and 44 are acquired. Then, the output values of
the temperature sensors 41, 42, 43, and 44 are used to obtain an
approximate expression for the measured temperature.
[0089] While there have been described what are at present
considered to be certain embodiments of the invention, it will be
understood that various modifications may be made thereto, and it
is intended that the appended claims cover all such modifications
as fall within the true spirit and scope of the invention.
* * * * *